This invention relates to a digital multiple reception apparatus and a digital multiple receiving method and, in particular, to a reception apparatus and a receiving method for realizing diversity reception in a code division multiple access (CDMA) communication.
In the manner which will later be described in conjunction with FIG. 1, a conventional diversity CDMA reception apparatus for the CDMA communication comprises a first and a second reception parts. Accordingly, the conventional diversity CDMA reception apparatus is disadvantageous in that it has a large mounted area and a lot of consumed current.
In addition, the diversity CDMA reception apparatus is different from a diversity time division multiple access (TDMA) reception apparatus for a TDMA communication. This is because the diversity CDMA reception apparatus carries out continuous reception operation while the diversity TDMA reception apparatus carries out reception operation in a time division fashion or intermittently reception operation. Accordingly, the diversity CDMA reception apparatus cannot adopt a structure or an antenna switching technique which is adopted in the diversity TDMA reception apparatus in the manner which will later be described in conjunction with FIG. 2. That is, if the antenna switching technique in the diversity TDMA reception apparatus is adopted in the diversity CDMA reception apparatus, the diversity CDMA reception cannot receive data at a time when antenna switching is carried out in a moment.
In addition, various prior arts related to the present invention are already known. By way of example, Japanese Unexamined Patent Publication of Tokkai No. Hei 5-206,903 or JP-A 5-206903 discloses “DIVERSITY DEVICE” to switch receiving antennas when a reception level drops to a level less than a prescribed one during the reception of a reception slot. According to JP-A 5-206903, a receiver selects a desired radio wave, outputs an IF signal and generates a reception field level. Sample and hold circuits hold the reception levels of the respective antennas before the reception slot and a first comparator compares the reception levels. A control circuit generates a branch control signal so that branch having a large level is selected each frame on the basis of the output of the first comparator and a switch timing signal generated immediately before the reception slot. A second comparator compares the reception field level in the reception slot with a reference voltage. When the reception field level in the reception slot becomes less than reference voltage, the reception level drop signal is switched and the control circuit switches the branch control signal based on the switching and switches the receiving antennas.
However, JP-A 5-206903 may disclose a diversity device for use in a TDMA system.
Japanese Unexamined Patent Publication of Tokkai No. Hei 9-331,282 or JP-A 9-331282 discloses “ANTENNA SWITCHING DIVERSITY CIRCUIT” to reduce the variation in the mutual coupling amount between two antennas in a miniaturized antenna diversity circuit. According to JP-A 9-331282, a combination of first through third switching circuits selects, as a selected antenna, one of a reception antenna and a transmission-reception antenna which receives a signal having the higher receiving electric field level and connects the selected antenna to a received signal input terminal of a reception circuit. A nonselected antenna is terminated by a terminator having nearly the same impedance as the input impedance of the received signal input terminal of the reception circuit. Consequently, the mutual coupling amount between the selected antenna and the circuit connected with the selected antenna, and the nonselected antenna and the circuit connected with the nonselected antenna, can always be made almost constant. It is possible to stabilize the maximum gain frequency and maximum gain of the reception antenna.
However, JP-A 9-331282 may disclose an antenna switching diversity circuit for stabilizing the maximum gain frequency and maximum gain of the reception antenna.
Japanese Unexamined Patent Publication of Tokkai No. Hei 6-268,635 or JP-A 6-268635 discloses “RADIO COMMUNICATIONS EQUIPMENT AND ANTENNA DIVERSITY METHOD FOR THE SAME” to provide an antenna diversity method for reducing the cost of the radio communications equipment, miniaturizing it by simplifying the configuration of a reception system, and exactly selecting an antenna system. According to JP-A 6-268635, at the radio communications equipment, a receiver and a demodulator are integrated into one system. Then, the measurement of received electric field strength and the collection of reception errors or the decision is accurately performed under the control of a microcomputer and a software memory inside a control part of the radio communication equipment so as to connect a first satisfactory antenna to the reception part of one system and, based on this result, antenna diversity is performed. Thus, there are advantages such as easily selecting/switching the antenna system used for receiving valid data and further preparing an optimum radio communications system.
JP-A 6-268635 may disclose an antenna diversity method for use in a TDMA/TDD radio communications system.
Japanese Unexamined Patent Publication of Tokkai No. Hei 9-36,843 or JP-A 9-36843 discloses “DIVERSITY RECEPTION CIRCUIT” to hold satisfactory reception quality and to retrieve an idle channel during communication without hit. According to JP-A 9-36843, first and second antennas, first and second reception demodulation parts, first and second synthesizers, a control part and a decoding part are provided. In a regular communication, the same selected frequency signals are outputted from both the first and the second synthesizers. Demodulation output from the reception demodulation part, which is related to a larger received electric field intensity, is given to the decoding part. In the case of retrieving the other idle channel or switching the channel, one synthesizer is caused to output the selected frequency signal of the channel in the middle of communication and the other synthesizer is caused to output the selected frequency signal of the channel of a switching destination.
JP-A 9-36843 may disclose a diversity reception circuit comprising two reception demodulation parts.
Japanese Unexamined Patent Publication of Tokkai No. Hei 11-55,728 or JP-A 11-55728 discloses “MOBILE RADIO SYSTEM” to improve the reliability of communication, the transmission efficiency and low power consumption by avoiding occurrence of intrusion of an interference wave with a simple configuration and to effectively utilize a frequency by using other communication carrier frequency on the occurrence of intrusion of the interference wave. According to JP-A 11-55728, in the system, a mobile terminal has first and second reception systems and a transmission system. The system adopts the after detection selection type space diversity method that selects one demodulation signal based on a level of an RSSI signal corresponding to the reception electric field strength of a received signal. The first and the second reception systems have a configuration of the double superheterodyne method. Furthermore, the communication system adopts the time division multiple access/frequency division duplex TDMA/FDD system, and a base station makes transmission by a TDM. In the case that the mobile terminal detects production of intrusion of an interference wave through one or both of an incoming frequency and an outgoing frequency with respect to the base station, occurrence of intrusion of an interference wave is reported to the base station. After the base station receives an intrusion occurrence notice of the interference wave from the mobile terminal, the base station assigns other time slot or a communication carrier frequency to the mobile terminal.
JP-A 11-55728 may disclose a mobile radio system comprising two reception systems having the configuration of the double superheterodyne method.